The effects of oxygen radical damage to proteins is largely unknown. The presence of iron inside cells can be detrimental to proteins if these iron stores become labilized (freed) in the presence of reducing equivalents and oxygen. The resultant damage to proteins mediated by Fenton chemistry can result in localized oxygen radical induced destruction in and around protein metal binding sites. A number of metal binding proteins were subjected to iron catalyzed oxidation, and concomitant losses of activity and structural changes were monitored. Glutamine synthetase, phosphoglycerate kinase, carbonic anhydrase, myoglobin and cytochrome b562 were the proteins used to explore the consequences of oxidative events. These proteins represent particular classes of proteins which can potentially serve as sites for oxygen radical production (i.e., metalloproteins, oxygen binding proteins and electron transfer proteins). Various physiochemical aspects of protein structure were examined before and after oxidation. Oxygen radical damage to these proteins ranges from substantial (multiple reactions observed along with loss of activity e.g. glutamine synthetase,phosphoglycerate kinase, Zn free carbonic anhydrase) to undetectable (e.g., myoglobin, cytochrome b562, Zn bound carbonic anhydrase).